Populations exposed to radiation are studied to quantify cancer risks and to understand carcinogenic mechanisms. Laboratory studies are incorporated into epidemiologic investigations. Staff serve on committees advising the government and international agencies. Recent findings indicate that (1) systemic chemotherapy combined with radiotherapy enhances the risk of leukemia in patients treated for non- Hodgkin's lymphoma; (2) radiotherapy for breast cancer and Hodgkin's disease increases the risk of lung cancer; smoking may enhance this risk; (3) radiotherapy for peptic ulcer increases the risk of stomach cancer, which is further increased after surgical treatment; (4) survivors of retinoblastoma are at a 30% cumulative risk for developing a second cancer by age 40; radiotherapy enhances this genetic susceptibility; (5) radiotherapy for endometrial cancer causes fewer leukemias than expected because of cell-killing and protraction; (6) radioactive iodine did not increase the risk of leukemia or thyroid cancer, suggesting that protraction of dose reduces risk; (7) breast cancer was not increased among medical technologists occupationally exposed to radiation; (8) the risk of radon-induced lung cancer among nonsmoking underground miners is greater than among smokers; risk decreases as the exposure duration shortens and with time since exposure; (9) a radon risk associated with indoor exposure, however, could not be detected in 4 large series; the level of risk may be too low to detect convincingly; (10) among A-bomb survivors, breast cancer risk was greatest for exposure before age 20; risk was remarkably high for early-onset breast cancer occurring before age 35, suggesting a genetic susceptibility; (11) radiation-induced thyroid cancer is rare for exposures after age 20; (12) quantitative estimates of risk for non-melanoma skin and liver cancers were made for the first time; (13) radiation-induced lung cancers tend to be of the small-cell subtype in both A-bomb survivors and uranium miners.